1. Field of the Invention
The subject invention relates to an improved idler roll for use with either a single or double facer corrugating apparatus and, in particular, to a fluid filled idler roll for use in tangential abutment with driven heated surfaces.
2. Description of the Prior Art
In process machinery it is common to place idler rolls against driven rolls in order to direct the flow of the medium being processed. It is also common, that these idler rolls are in abutment with heated rolls, or similarly, idly roll against a heated surface. These idler rolls are generally comprised of a solid steel material, pivotally fixed at their ends adjacent to the cooperating heated surface.
A problem presently plaguing the process machinery industry is thermal distortion of these rolls along their longitudinal length, causing a bowed configuration of the idler roll. This distortion is more prevalent upon restarting of the equipment after a shutdown, where the idler rolls were in edgewise engagement with a heated surface over an extended period of time.
For example, in some equipment, these idler rolls are precision crafted, where rolls exceeding six feet in length must be held within tolerances of 0.001 inches in runout. However, it is not uncommon that, after an extended shutdown, the distortion along the longitudinal length can approach 0.060 inches in runout.
To exaggerate the problem further, upon startup of the machinery, the idler rolls remain distorted for long periods of time, possibly up to 30 minutes or longer; and during such time, the idler rolls are in distorted engagement against the heated surfaces causing uneven wear of both the idler roll and the mating surface. Furthermore, if the paper web is fed between the idler roll and the heated surface, it could be unevenly pressurized, or worse yet, it could be crushed by the bowed idler roll.
By way of example, a single facer apparatus for producing single faced corrugated board produces corrugated flutes from a flat web of paper medium by feeding the flat web through the nip point of two meshing corrugating rolls, typically an upper and lower roll. To adhere the corrugated medium to a first liner paper, the single facer includes a heated pressure roll in tangential abutment with the lower corrugating roll, and the flute tips of the medium web are coated with adhesive and merged together with the liner web, between the lower corrugating roll and the pressure roll. During the transfer of the corrugated medium from the nip point between the two corrugating rolls, to the nip point between the lower corrugating roll and the pressure roll, it is important that the flutes of the medium remain within the corresponding corrugations of the corrugating roll.
To this end, it is common to form a pressurized chamber around at least the lower corrugating roll, such that the formed medium is forced against the lower corrugating roll to retain the formed flutes within the corrugations of the lower corrugating roll. A seal roll is placed in tangential abutment with the heated pressure roll, to seal the pressure chamber effectively along the longitudinal length of the pressure roll.
In the manufacturing of corrugated paper, it is common to have extended periods of time, where the single facing apparatus is idle. This could be due to a paper jam, or could simply be a changing of the paper size to vary the thickness and rigidity of the corrugated board. During such time, the heated corrugating rolls and the heated pressure roll, remain heated, as the heat up time for these rolls is quite lengthy due to their size.
When the single facer corrugating apparatus is stopped, a longitudinal edge of the seal roll is pressed against the heated pressure roll, with the liner paper therebetween. This contact causes heating of the roll along the longitudinal edge resulting in thermal distortion of the seal roll along the longitudinal length. The thermal distortion causes the seal roll to take on a bowed configuration, having an eccentric central portion facing the heated pressure roll.
When the machine is once again started, this bowed configuration causes engagement of the eccentric portion with the pressure roll which results in uneven sealing of the pressurized air along both the seal roll and the pressure roll. The engagement of the eccentric portion against the pressure roll can also tear or weaken the liner paper at the eccentric portion, which continues until the seal roll is uniformly heated. A tearing of the liner paper results in unnecessary downtime and a waste of paper.
In another example, a double facer apparatus produces double faced corrugated board by feeding the single faced corrugated board to the apparatus and merging it with a second liner paper, with adhesive therebetween. In order to cure the adhesive, an array of steam heaters are aligned in side-by-side registration, and the single faced corrugated board and second liner paper are pulled over the upper surface of the heaters. To assist in the heat transfer, pressure is applied to the second liner and the single faced board, by placing a continuous belt over the single faced corrugated board with weight rolls positioned above the belt.
A similar thermal distortion phenomenon occurs with the weight rolls on the double facer apparatus, as occurs with the seal roll on the single facer. When the double facer apparatus is shut down for any length of time, a longitudinal edge of the weight rolls is in contact with the continuous belt. Due to the proximity of the belt to the heaters, the belt is also heated, and the contact between the weight rolls and the belt causes thermal distortion of the weight rolls along their length.
Once again, on start-up, the rolls are distorted, thereby causing the rolls to pressurize the continuous belt unevenly against the corrugated board. Although the purpose of the rolls above the belt is to urge the corrugated board against the heaters to increase the heat transferred to the corrugated board, the bowed rolls result in uneven heating of the double faced corrugated board. When the bowed roll faces away from the belt, the rolls are not pressing the board against the heaters except at the edges. Worse yet, as the bowed rolls rotate one-half turn, the bowed configuration faces the belt, possibly crushing the center portion of the corrugated board beneath the belt. Crushing of corrugated board is detrimental to its utility, as the board is weakened along the lengths of the corrugated flutes, and is more likely to bend along the flutes, or buckle when stacked.
In the above referenced examples, in both the single factor and double facer apparatus, the cause of the distortion in the idler rolls is the extended contact between a longitudinal edge of the solid steel idler roll against the heated surface during the machinery shutdown. This causes an edge of the idler roll to have a higher temperature than that of the remainder of the idler roll. This problem is exaggerated by the inability to equalize the temperature rapidly in the idler roll upon start-up, resulting in a continued distortion of the idler rolls well into the process cycle. As mentioned above, this distortion can continue for a long period of time.